1. Field of the Invention
The present invention relates to, e.g., an exposure apparatus for exposing a substrate to light to manufacture a device, such as a semiconductor device or a liquid crystal display device and, more particularly, to an exposure apparatus using a liquid immersion method.
2. Description of the Related Art
A process for manufacturing a semiconductor device formed from the micropattern of an LSI or a VLSI adopts a reduction projection exposure apparatus, which reduces a pattern formed on a mask and projects and transfers it onto a substrate coated with a photosensitive agent. As the degree of integration of a semiconductor device increases, further micropatterning becomes necessary. The exposure apparatus has coped with micropatterning at the same time as the development of the resist process.
As an implement for increasing the resolution of an exposure apparatus, it is common practice to shorten the exposure wavelength or to increase the numerical aperture (NA) of a projection optical system.
As for the wavelength of exposure light, a shift from a 365-nm i-line to KrF excimer laser light having an oscillation wavelength around 248 nm is in progress, and an ArF excimer laser having an oscillation wavelength around 193 nm is under development. A fluorine (F2) excimer laser having an oscillation wavelength around 157 nm is also under development.
On the other hand, a projection exposure technique using a liquid immersion method as a technique for increasing the resolving power independently of the above methods is receiving a great deal of attention. The conventional methods fill, with a gas, the space between the last surface of a projection optical system and the surface of an exposure target substrate (e.g., a wafer). However, the liquid immersion method executes projection exposure while filling that space with a liquid. Assume, for example, that the liquid immersion method uses pure water (refractive index; 1.33) as the liquid to be supplied to the space between the projection optical system and the wafer, and sets the maximum incident angle of a light beam imaged on the wafer equal to that in the conventional methods. In this case, the liquid immersion method can advantageously attain a resolution 1.33 times that in the conventional methods, even by using a light source having the same wavelength. This amounts to increasing the NA of the projection optical system in the conventional methods to 1.33 times. The liquid immersion method can attain a resolving power whose NA is one or more, which is practically impossible in the conventional methods.
An attempt to apply the liquid immersion method to an exposure apparatus is recently in progress (Japanese Patent Application Laid-Open No. 06-124873).
FIG. 8A is a view showing the structure of the exposure apparatus disclosed in Japanese Patent Application Laid-Open No. 06-124873.
Referring to FIG. 8A, an illumination optical system 103 illuminates the pattern of a reticle 101 to project and to form by exposure that pattern on a wafer 102 through a projection optical system 104. A reticle stage 105 moves the reticle 101. Filling a liquid tank (chamber) 109 with a liquid 130 provides the ability to fill, with the liquid 130, the space between the wafer 102 and the end face (optical element 107) of the projection optical system 104. The liquid tank 109 accommodates a wafer conveyance device, wafer chuck 112, X-Y stage 113, fine moving stage 114, and part or all of each of coarse alignment devices 111-1 to 111-4. The wafer conveyance device loads the wafer 102 from a wafer cassette 110 and sets it on a wafer chuck 112. Reference numeral 115 denotes a laser interferometer. A reference mirror 116 is attached to the surface of the fine moving stage 114 along the X and Y directions (the Y direction is not shown), and reflects light from the laser interferometer 115 to measure the position of the fine moving stage 114. The liquid tank 109 has a window 117 to pass light from the laser interferometer 115. A heat-insulating material 118 is formed outside the liquid tank 109 and thermally insulates it from outside.
As shown in FIG. 8B, Japanese Patent Application Laid-Open No. 06-124873 describes another arrangement example of the exposure apparatus designed to mount the liquid tank 109 on the fine moving stage 114 while placing, in the liquid tank 109, only constituent parts including the wafer chuck 112 or while directly placing the wafer chuck 112 on the bottom surface of the liquid tank 109. That is, Japanese Patent Application Laid-Open No. 06-124873 describes the exposure apparatus using a method of mounting, in the liquid tank 109, the whole wafer 102 and the end face of the projection optical system 104.
WO99/49504 shows another example in which the liquid immersion method is applied to an exposure apparatus. WO99/49504 describes a method of supplying a liquid to only the space between a projection optical system and the surface of a wafer so as to fill that space.
FIG. 9 is a block diagram showing the arrangement of an inline connection between an exposure apparatus and a coating/developing device. Upon receiving a wafer from a coating/developing device 122, a wafer conveyance robot of an exposure apparatus 123 transfers that wafer to an exposure stage 125. The same robot also transfers an exposed wafer to the coating/developing device 122. Even in the coating/developing device 122, a robot to transfer a wafer coated with a resist to an exposure apparatus side interface unit 124 transfers the exposed wafer to a heater (Japanese Patent Application Laid-Open No. 2002-57100).
Unfortunately, the conventional exposure apparatuses suffer from local defocusing, which arises from the dropping, onto the wafer chuck, or the like, upon wafer transfer, of a liquid adhering to the surface of the wafer. This results in a decrease in yield. Furthermore, the wafer chuck requires replacement while stopping the apparatus for a long period of time, which has a great influence on the device production. When the robot transfers an exposed wet wafer, the liquid adheres to its hand and then adheres to an unexposed wafer to be transferred next. This may cause transfer of foreign substances among wafers (to be referred to as cross-contamination hereinafter). As a consequence, local defocusing arises, resulting in a decrease in yield.
Furthermore, when the robot transfers a wafer having a liquid adhered on it to the coating/developing device to heat that wafer, temperature non-uniformity occurs due to heat generated as the liquid evaporates. This degrades the CD uniformity. On the other hand, the practical application of high-speed spin drying in consideration of a case wherein all exposed wafers are wet complicates the structure of the exposure apparatus. This increases the cost and decreases the throughput as well.